Krypton and xenon are undergoing increasing demand in a number of applications. Krypton is being widely used in high quality lighting including long-life light bulbs and automotive lamps. Xenon is being used for medical applications including special X-ray equipment. Both of these gases are commonly used in many laboratory and research applications.
The principle source of krypton and xenon is the atmosphere. Atmospheric air contains about 1.1 ppm (parts per million) of krypton and about 0.08 ppm of xenon. Generally, krypton and xenon are recovered from the air in conjunction with a comprehensive air separation process which separates air into oxygen and nitrogen.
Due to the lower vapor pressures of krypton and xenon these gases concentrate in the oxygen rather than in the nitrogen during the air separation. The concentration of the atmospheric krypton and xenon in the oxygen increases their concentration by a factor of five because oxygen comprises only about one-fifth of the atmospheric air.
The air separation process may produce gaseous or liquid oxygen, or may produce both, and the krypton and xenon will concentrate in either oxygen product. It is desirable to further concentrate the krypton and xenon so that their separation from oxygen can be carried out efficiently. When the krypton and xenon are recovered in gaseous oxygen, and krypton-xenon concentration process must be carried out at the same time as the air separation process because it is impractical to store gaseous oxygen in the quantities produced by an air separation plant. It may thus be desirable to recover the krypton-xenon in liquid oxygen from an air separation plant, since this liquid can be stored and can be combined with other such liquids from other distant air separation plants to form a feed for a krypton-xenon concentration process.
However, removing liquid oxygen from an air separation plant is costly because of the associated refrigeration which is removed from the air separation plant with the liquid oxygen. It is thus desirable to have a krypton-xenon concentration process which uses a liquid feed but which also produces a liquid rare gas-free product.
As is known, oxygen can be hazardous if not handled properly. Therefore, known krypton-xenon concentration processes employing a liquid feed have heretofore been quite complicated in order to achieve the desired krypton-xenon concentration with the requisite safety. It is desirable therefore to provide a process which effectively concentrates krypton and xenon employing a liquid feed without the heretofore necessary excessive complications occasioned by the handling of oxygen.
It is therefore an object of this invention to provide an improved process to produce a krypton-xenon concentrate.
It is another object of this invention to provide an improved process to produce a krypton-xenon concentrate employing a liquid feed.
It is a further object of this invention to provide an improved process to produce a krypton-xenon concentrate which also produces a rare gas-free liquid product.
It is yet another object of this invention to provide a process to produce a krypton-xenon concentrate which can carry out the desired concentration without all the heretofore necessary complications of known processes.